The present invention relates to a mesh and more particularly to a mesh having varying degrees of electron permeability over its surface used in an electron discharge tube.
Meshes on dynodes used in electron discharge tubes are well known in the art. Heretofore, such meshes have been made from a network of conducting elements intersecting to openings of uniform sizes. The easiest, simplest and most widely used mesh is a planar network composed of mutually orthogonal rectilinear conducting elements. In general a mesh must serve two functions. The first is to permit the passage of primary electrons through the mesh to impinge on the active area of the dynode. The second function is to provide a field within the cavity of the dynode to direct the secondary electrons released from the dynode onto the next dynode or anode. In creating the cavity, the mesh must shield the secondary electrons from the field of the source of primary electrons.
These two functions, however, are highly competitive and compromises are often made. At one extreme if one desired solely to have all the primary electrons impinge on the dynode, then no mesh ought to be placed in the path of the primary electrons. The mere presence of a member, even though full of openings, in the path of the primary electrons raises the probability of a primary electron hitting the mesh and being deflected or stopped from impinging on the dynode. However, the absence of a mesh, means that no secondary electrons can be released from the dynode, because the field of the source of the primary electrons is negative compared to the dynode. This negative field prevents the release of secondary electrons from the dynode. At the other extreme, if one desired solely to have all the secondary electrons directed to the next dynode or anode, and to shield all of the secondary electrons from the field of the source of primary electrons then a conducting plane ought to be placed in the path of the primary electrons to stop all of the field of the source of primary electrons. This, of course, means that no primary electron would ever be incident upon the dynode. Heretofore, because meshes have been planar networks comprising mutually orthogonal rectilinear conducting elements forming uniform openings, the size of the opening or the optical transmissive per unit area of the mesh has been the means by which the mesh can be adjusted to accomodate the two competing functions. The adjustment of the opening size however is accomplished while maintaining the uniformity of the size of the openings.